scholarly journals Profile vortex shedding from low-speed axial fan rotor blades: a modelling overview

Author(s):  
Gábor Daku ◽  
János Vad

This paper presents an overview of the characteristics potentially influencing the profile vortex shedding (PVS) phenomenon being relevant in noise and vibration of low-speed axial fan rotor blades. Dimensional analysis has been applied to explore the essential dimensionless quantities in a systematic and comprehensive manner. On this basis, limitations have been established, and simplifying assumptions have been set up in terms of PVS investigation. Groups of dimensionless characteristics playing a role in the semi-empirical model for predicting the PVS frequency were identified. The available semi-empirical model and its unique features related to the measurement evaluation methodology and Reynolds number dependence have been outlined. The presented comprehensive analysis provides guidelines from the perspective of transferability of the literature data on PVS from steady, isolated blade profile models to low-speed axial fan rotors. It also results in the formulation of objectives of future research related to PVS.

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Gábor Daku ◽  
János Vad

Abstract This paper presents hot-wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for the consideration of profile VS in preliminary design of axial fans in the moderation of VS-induced blade vibration and noise emission.


Author(s):  
Gábor Daku ◽  
János Vad

Abstract The paper presents hot wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds-number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt-trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for consideration of profile VS in preliminary design of axial fans in moderation of VS-induced blade vibration and noise emission.


Author(s):  
Gábor Daku ◽  
János Vad

This paper presents a critical overview on worst-case design scenarios for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in twofold approaches of blade mechanics and aerodynamics. For these purposes, the frequency of the first bending mode of a plate of arbitrary circular camber is expressed by modeling the fan blade as a cantilever beam. Furthermore, an iterative blade design method is developed for checking the risky scenarios for which spanwise and spatially coherent shed vortices, stimulating pronounced vibration and noise, may occur. Coupling these two approaches, cases for vortex-induced blade resonance are set up. Opposing this basis, design guidelines are elaborated upon for avoiding such resonance. Based on the approach presented herein, guidelines are also developed for moderating the annoyance due to the vortex shedding noise.


1987 ◽  
Vol 109 (3) ◽  
pp. 282-288 ◽  
Author(s):  
R. D. Blevins ◽  
M. M. Bressler

In the first part of this series, experimental data were presented which suggest that the acoustic resonance in heat exchanger tube bundles is tied to periodic vortex shedding from the tubes. In this paper, a semi-empirical model for predicting the onset of resonance is developed. This model is compared with experimental data and other models from the literature. Methods of suppressing the resonance are developed and experimental data on their effectiveness are presented.


10.28945/4314 ◽  
2019 ◽  

Aim/Purpose: The goal of this study is to advance understanding of ICT utilization by SMMEs by checking access, ability (in terms of technological skills) and usage of ICT among some SMMEs entrepreneurs operating their businesses in an underdeveloped areas to enhance their business activities in order to utilizes the digital opportunities 21st century digital economies present. Background: In today’s world no nation or region is untouched by the forces of globalization and digital economy. One of the key pioneering forces of globalization is the advances of ICT like internet, social networks, etc. In the sphere of business, this pioneering force has also altered the way businesses and organizations communicate and interact with customers and society at large. Such alternation presents obvious opportunities for wealth creation and growth for businesses and organizations that are well-equipped to take advantages of them. But for those that are less-equipped, particularly SMMEs, globalization can easily lead to fore-closures and marginalization. It is a common knowledge that SMMEs entrepreneurs mostly rely on ICT gadgets like mobile phone, Laptops, Tablets to conduct their business activities as many of them don’t have enough capital to set up offices with necessary equipment. Therefore, using various ICT functions/programs on these ICT devices to enhance their business activities are critical to their businesses in the 21st century digital economies. Methodology: Purposeful sampling was used to approach fifty-four SMMEs entrepreneurs operating their businesses in underdeveloped areas locally called Townships in Buffalo City Metropolitan. Microsoft excel was used in the descriptive statistics. Contribution: This research will add to the growing knowledge ICT usage in SMMEs in the 21st century digital economies. Findings: The results indicate that the participating SMMEs entrepreneurs need to be educated, trained and supported in the use of the ICT applicable to enhance their business activities in order for them to take advantages of 21st century digital economies present. Recommendations for Practitioners: The agencies tasked with looking after SMMEs in South Africa needs to consider the lacked of utilisation of ICTs by SMMEs entrepreneurs operating their businesses in underdeveloped areas as one of the barrier to growing of their businesses and take necessary steps to address it. Recommendation for Researchers: Since age and gender have been proven to be key-moderating variables in many technology acceptance models. There is a need to explore in depth whether the factors of gender and age also act as barriers. Impact on Society: The research will assist stakeholders, policy makers and agencies tasked with looking after SMMEs to identify the barriers hindering SMMEs to grow and address them accordingly. Future Research: More work needs to be done to check whether gender, age of the SMMEs entrepreneurs have some effects on their attitude towards the integration of ICT into their business activities.


Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 412
Author(s):  
Shao-Ming Li ◽  
Kai-Shing Yang ◽  
Chi-Chuan Wang

In this study, a quantitative method for classifying the frost geometry is first proposed to substantiate a numerical model in predicting frost properties like density, thickness, and thermal conductivity. This method can recognize the crystal shape via linear programming of the existing map for frost morphology. By using this method, the frost conditions can be taken into account in a model to obtain the corresponding frost properties like thermal conductivity, frost thickness, and density for specific frost crystal. It is found that the developed model can predict the frost properties more accurately than the existing correlations. Specifically, the proposed model can identify the corresponding frost shape by a dimensionless temperature and the surface temperature. Moreover, by adopting the frost identification into the numerical model, the frost thickness can also be predicted satisfactorily. The proposed calculation method not only shows better predictive ability with thermal conductivities, but also gives good predictions for density and is especially accurate when the frost density is lower than 125 kg/m3. Yet, the predictive ability for frost density is improved by 24% when compared to the most accurate correlation available.


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